During the manufacture of semiconductor devices, materials which have been deposited on the face of the semiconductor wafer must be removed. Typically these surface materials are removed through the use of a standard chemical bath system consisting of an open rectangular quartz container filled with a chemical solvent or etchant, such as acid. Performance of the standard chemical bath system is limited by the continual need to replace the chemical solvent as the solvent becomes contaminated. Filtered constant bath systems offer increased performance over standard bath systems by reducing the time and volume of chemicals necessary for replacing contaminated solvent in a standard bath system. In a filtered bath system, the solvent typically is pumped from the tank through a drain and passed through a filter to remove the unwanted particulate contaminants.
One filtered bath system is the fixed weir overflow bath system with gutter illustrated in FIG. 1. The fixed weir bath system with gutter is typically manufactured by welding an L-shaped quartz structure (the gutter) to the top of a rectangular quartz container. Although the bath system is a single container, the container can be divided into an upper and lower tank region. The open quartz container forms the lower tank region and is used for wafer processing. The L-shaped quartz structure welded to the quartz container forms the upper tank or gutter region.
The first step in manufacturing the fixed weir bath system with gutter is to scallop the open top edge of the rectangular quartz container. This scalloping procedure is typically performed by a laser. The scallop shape determines the fluid flow characteristics of the bath system. Next, the upper tank or gutter region is formed by welding an L-shaped quartz structure to the scalloped lower tank region. The weld of the L-shaped structure to the lower tank region must be slightly below the bottommost edge of the scallops. By positioning the weld below the scalloped edge of the lower tank region, fluid can flow over the scalloped edging from the lower tank processing region into the upper tank gutter region.
In operation the fixed weir bath system with gutter is filled with solvent. As more solvent is pumped into the container, solvent overflows the scalloped edges of the lower tank processing region into the upper tank or gutter region. Particulate which fall onto the surface of the solvent are trapped by the surface tension and removed by the overflow action into the gutter before the particulate can sink into the liquid and contaminate the solvent. The gutter region has a drain through which the solvent is removed, filtered and pumped back into the container.
Although the fixed weir bath system with gutter offers good performance it is expensive to manufacture. Welding the L-shaped structure to the quartz container to form a gutter produces a weak weld which is prone to breakage. Breakage occurring at this point in the manufacture process adds greatly to manufacturing costs. Material costs are increased since the quartz rectangular container and gutter structure cannot be salvaged. Furthermore, disposal of the bath system is especially expensive at this point in the manufacture since labor costs from scalloping the quartz container and welding the gutter region have already been incurred and must be added to the bath system cost.
Another disadvantage of the fixed weir overflow bath is its lack of flexibility. The scalloped edges of the lower tank region cannot be changed once the bath system has been manufactured. Thus, if new processing characteristics are desired, the user must replace the entire bath system instead of simply replacing the scallops. This replacement of bath systems is especially expensive when the user is in the process development stage and is experimenting to determine the optimal scallop characteristics for a new semiconductor wafer process.